The field of the invention is the recovery of cobalt catalyst used in the oxo process.
The state of the prior art of the oxo process and the recovery of cobalt catalyst used therein may be ascertained by reference to the Kirk-Othmer "Encyclopedia of Chemical Technology", Vol. 14 (1967) under the section OXO PROCESS, on pages 373-390, particularly pages 375-376, which disclose the cobalt catalysts, and pages 383-384, which disclose the catalyst removal and recovery, and U.S. Pat. Nos. 2,767,048, 2,816,933 and 2,841,617 of Joseph K. Mertzweiller which issued Oct. 16, 1956, Dec. 17, 1957 and July 1, 1958 respectively.
Cobalt carbonyl compounds are used as catalysts in oxo reactions. The cobalt catalyst must be removed from the reaction product in order to avoid impurities which would disrupt reactions employing the compounds. This removal method is called "cobalt removal". One of the products of "cobalt removal" is a water solution of a cobalt salt. The cobalt compound (carbonyl) must be recovered in an active form in order to be reintroduced into further oxo methods in order to be economically feasible.
The recovery is obtained by contacting the cobalt salt solution with carbon monoxide and hydrogen (usually water gas) under high pressure and temperature in the presence of a solvent for the cobalt hydrocarbonyl produced in the reaction.
U.S. Pat. No. 2,767,048 of Joseph K. Mertzweiller which issued Oct. 18, 1956 discloses the process of preparing and separating an aqueous solution of a cobaltous salt of cobalt hydrocarbonyl suitable for catalyzing a reaction of an olefinic carbon compound with carbon monoxide and hydrogen. An aqueous solution of cobaltous acetate, which supplies Co.sup.++ ions, is initially treated with a gaseous mixture of hydrogen and carbon monoxide in the presence of an inert oxygenated organic solvent therefore which is an aldehyde or an alcohol having at least 4 carbon atoms such as iso-octyl aldehyde or iso-octyl alcohol. This is done prior to contacting the solution with the olefinic carbon compound. The treatment takes place at a temperature between about 90.degree. C and 180.degree. C and a pressure of 1000 to 4000 p.s.i.g. The cobaltous acetate is maintained in the reaction mixture in amounts such that it provides Co++ ions at least in sufficient amounts to combine with all Co(CO.sub.4) ions present in the aqueous phase. The unconverted gases are discharged from the resulting reaction mixture. The two phases of the reaction mixture are separated into an organic solvent phase and an aqueous phase containing the cobaltous salt of cobalt hydrocarbonyl. The aqueous phase containing the cobalt salt of cobalt hydrocarbonyl is then withdrawn. This aqueous phase containing the cobalt salt of cobalt hydrocarbonyl is not suitable for hydroforming of higher olefins (C.sub.6 or higher) because of low miscibility with the oxo reaction mixture.
Because of this, the catalyst must be used with a solvent for the oxo reaction mixture. The cobalt formed in the organic phase in these methods is dicobalt octacarbonyl.
According to British Pat. No. 702,221, aromatic hydrocarbons, liquid olefins, cycloparaffins, ether, esters, alcohols such as octanol as well as high boiling point by-products of the oxo reactions are suitable for solvents for the dicobalt octacarbonyl. Aldehydes having 4-8 carbon atoms have been suggested for the same purpose by German Published Application (DT-AS) 1,767,277.
These methods have certain known inherent disadvantages such as the formation in the oxo reaction of a whole series of side products.